Chairs having an adjustable back are popular because the sitter can adjust the back to a desired position for him/her to sit on the chair comfortably.
Many adjustment devices for a chair back have been devised, each of them having its own features, such as those disclosed in U.S. Pat. No. 5,169,257, U.S. Pat. No. 4,294,488, U.S. Pat. No. 5,590,932 and No. U.S. Pat. No. 5,205,609.
The present invention is aimed to provide an adjustment device for a chair back, of which the design is different from the above said prior art ones.